In optical communication that can transmit optical information obtained by photoelectrically converting large-volume digital information at a high speed by using an optical fiber, an optical communication module is used for optically coupling the optical fiber with a photoelectric conversion element of either one of a light emitting element and a light receiving element fitted in the photoelectric conversion element package.
As this type of optical communication module (optical module), various structural forms have been developed. As a conventional example, there is one in which an aspherical lens and a holder are integrally molded from plastic, and a photoelectric conversion element package is housed opposite to the aspherical lens in a cylindrical portion of the holder (for example, see Patent Citation 1).
FIG. 1 is a longitudinal sectional view showing a conventional optical module.
The conventional optical module 100 shown in FIG. 1 is disclosed in Patent Citation 1, and is explained briefly with reference to Patent Citation 1.
As shown in FIG. 1, the conventional optical module 100 includes a photoelectric conversion element package 110 in which a photoelectric conversion element 112 is fitted to one side 111a of a housing 111, and a holder 115 arranged on the one side 111a of the housing 111 of the photoelectric conversion element package 110 for being coupled with an optical fiber (not shown), and including an aspherical lens 115g integrally molded therewith (which is described later). The holder 115 is assembled so as to be engaged with upper and lower sides 111b and 111c of the housing 111 of the photoelectric conversion element package 110.
First, in the photoelectric conversion element package 110, a photoelectric conversion element 112 of either one of a semiconductor light emitting element (semiconductor laser) and a semiconductor light receiving element (photo diode), is fitted to the one side 111a of the housing 111, and a lead 113 connected to the photoelectric conversion element 112 is protruded from the other side 111d, which is opposite to the one side 111a of the housing 111.
Next, the holder 115 is formed by injection molding, using light transmitting plastic (for example, PEI, PC, or PMMA). A stepped hole 115b with a bottom for fitting the optical fiber is formed on one side 115a, and the other end face 115c is formed as a cylindrical portion 115d. A depression 115e is formed for housing the photoelectric conversion element package 110 inside of the cylindrical portion 115d, and the aspherical lens 115g is integrally molded on a partition wall 115f positioned between the stepped hole 115b with a bottom and the depression 115e, so that a convex curve of the aspherical lens 115g protrudes into the depression 115e. 
Further, the holder 115 and the photoelectric conversion element package 110 are engaged with each other and assembled together, so that when the photoelectric conversion element package 110 is housed in the depression 115e of the holder 115, the aspherical lens 115g integrally molded in the holder 115 faces the photoelectric conversion element 112 fitted to the one side 111a of the housing 111 of the photoelectric conversion element package 110 with a gap therebetween, an apex P1 and a focal point P2 of the aspherical lens 115g are on an optical axis K of the photoelectric conversion element package 110, and the focal point P2 of the aspherical lens 115g approximately matches a light emitting point or a light receiving point of the photoelectric conversion element 112.
According to the conventional optical module 100, therefore, even if ambient temperature changes, the position of the focal point P2 of the aspherical lens 115g integrally molded in the holder 115 approximately matches the light emitting point or the light receiving point of the photoelectric conversion element 112 fitted to the one side 111a of the housing 111 of the photoelectric conversion element package 110. Therefore, optical coupling efficiency is improved, thereby enabling efficient optical communication. The foregoing is described in Patent Citation 1.    Patent Citation 1: Japanese Patent Application Laid-open No. 2005-326884